Popular Science Monthly/Volume 7/August 1875/The Glaciers of Norway
|THE GLACIERS OF NORWAY.|
A VISIT to Switzerland has of late become so easy and frequent an undertaking, that the glaciers around Mont Blanc and the Jungfrau have lost much of their romance and all their novelty. Every tourist climbs the Montanvert to enjoy the sensation of walking over the Mer-de-glace in midsummer, and creeps under the Rosenlaui to admire the deep-blue color of its icy vault. There is, however, another country which, in the number and beauty of its glaciers, is a formidable rival of Switzerland; but, lying as it does, out of the ordinary track of pleasure-travel, is far less known or appreciated. Norway may, in fact, be styled with good reason the country of the glacier. True, the height of its mountains does not approximate to that of the Alps. Only one or two summits exceed 8,000 feet in altitude, and this elevation is not much more than half that of Mont Blanc. But almost the entire country stands high above the level of the ocean, while its situation so far toward the north enables the snowfields, which are the feeders of the glaciers, to retain their vast accumulations with little loss though rain or thaw.
If the reader will glance at a map of Norway, he will see that there are two well-defined divisions: the southern, a region not destitute of flourishing cities and towns; and the northern, a narrow strip consisting of little more than a succession of headlands and islands, stretching far within the Arctic Circle. Both divisions have their characteristic, that the mountain-ranges rise in the form of wide tablelands, extending for long distances in so nearly a perfect level "that, did roads exist, a coach-and-four might be driven along or across them for many miles." The very valleys that break up their continuity are unperceived by the eye, being overlooked on account of their narrowness; and the view is interrupted, only by slight undulations, or by occasional mountains of no great size. Here it is that, summer and winter, the moisture which elsewhere descends in the form of rain, spreads the successive layers of the great Sneefon. Prof. Forbes, in the map accompanying his interesting work on "The Glaciers of Norway," indicates not less than eighteen of these "chief permanent snowfields" to the south of Trondhjem, and nineteen in the narrow strip north of that city. It must not, however, be concluded too hastily that the climate of Norway is cold and inhospitable; for no greater contrast can be found between countries lying in the same latitude, than between Norway and Greenland. The influence of the Gulf Stream is nowhere more strikingly traced; for, if the summers in Christiania are comparatively cool, the winters are as warm as in many places far to the south of it. Indeed, it is the remarkably equable temperature of Norway which, while it prevents the harbors from being closed by drifting ice, like those of the opposite shores of Greenland, yet, allows the line of perpetual snow to come down as low as 4,000 or 5,000 feet above the sea-level. For it has been conclusively proved that it is not so much the intensity of the winter's cold, as the amount of the summer's heat, that fixes the point where frost reigns supreme throughout the year. So it happens that, while the haven of Bergen, in latitude 60°, is frozen over only twice or three times in a hundred years, or about as often as the same fate befalls the Seine at Paris, the eternal snows cover the mountain-sides in the neighborhood of Bergen at heights at which the peasant on the Jura or the Alps pastures his flocks through the long summer months.
Of late, the savants of Norway have been giving to the world the results of observations upon the glaciers which they enjoy such remarkable facilities for examining. About 175 miles in a direct line to the northwest of Christiania (which is not only the capital of Norway, but the seat of one of the best universities of Europe) is a spur of the principal range included between the two inlets of Sogne and Nord—fiords. Upon its top is the largest snow-field of Norway, which bears the name of Justedal (Jostedalsbræen). Its superior magnitude and its comparative nearness to Christiania have led to its selection by two of the most eminent geologists of the country as a subject of special study. In 1869 Prof. Sexe published, as the "Programme" of the university for the first semester of the preceding year, a paper on the great glacier of Boium; and, in 1870, M. C. de Seue, of the Meteorological Institute, gave to the world, as the "Programme" for the second semester of that year, a more extended account of his observations under the title of "Le Névé de Justedal et ses Glaciers." Some of the results of the researches of these gentlemen may be of interest even to those who would soon grow weary of purely scientific details.
This immense field of snow and ice measures over forty miles in length from northeast to southwest, and from four to seven miles or more in breadth, covering, with its dependencies, according to M. de Seue's calculations, not less than some 550 square miles. The névé, or snow-field proper, is by no means a dead level, but the inequalities of the rocky crags are, for the most part, concealed by the thick deposit of snow, which is supposed to be at least 150 feet deep on the average, while in places it certainly fills up depressions of twice that depth. Here the snow is granular, lying in distinct layers, the product of the storms of successive seasons, and rent with frequent fissures. The glaciers spring from the edge. Wherever the jagged cliffs with which that edge bristles fall away and leave ravines, there the snow-field seeks an outlet. The glaciers are, as it were, the rills by which the great perennial reservoir discharges into the valleys below. So numerous are they, that their exact number has never been ascertained. Of glaciers of the first class, or those which pour their icy streams quite down into the valley, there are twenty-four; but, if we also include in the enumeration the glaciers of the second class, or those which remain suspended on the mountain-sides, the number is counted by hundreds. Some of the second class, it may be noticed, seem almost entitled, by reason of their breadth and depth, to be included in the higher class.
Each glacier presents many of the same phenomena as all the rest. From the moment it leaves the parent névé, or snow-field, the constitution of the mass is different from that of recently-fallen snow. Compressed by the immense weight of the superior strata, that lower portion of the névé which feeds the glacier is, at the very start, transformed into a solid ice, whose particles are cemented by the alternate melting and freezing which go on through all but the coldest weather of the year. Whether it is the pressure of the névé, or the irresistible expansion caused by the action of cold upon the water pervading its great mass, that drives off the glacier, is a question respecting which the most intelligent observers are by no means unanimous. Against the theory of weight as the motive power is urged the fact that occasionally the glaciers are not strictly adjacent to the superior snowfield, but separated from it by an intervening space of bare rock. When once it has emerged from the névé, the glacier becomes a stream of ice chiefly distinguished from a fluid river by the greater sluggishness of its current. How, it may be asked, can a mass of solid ice move in a fixed channel? The question was long unanswered. Indeed, it was only slowly that the truth forced itself upon the scientific world that it does actually move at all. And, the fact being conceded, the explanation is still not altogether easy. Prof. Sexe imagines that the plastic character of the glacier, as he has observed it in the neighborhood of Justedal, resides in the ease with which the ice fractures and the equal facility with which it reunites when fragments are brought together. Thus it is that, under the immense weight of the glacier, the glassy material of which it is composed is rent when brought into contact with some solid rock standing in its bed, and that the parted streams become one again as soon as the obstacle in their way is passed. So also it is that longitudinal fissures regularly form in the lower part of the glacier of Boium, when the glacier reaches a point where it can expand in the less contracted valley, while transverse fissures open in the glacier of Suphelle at a place where the inclination suddenly becomes more considerable than it was at first, and close up as soon as the slope is again a gentle one. M. de Seue, on the other hand, emphasizes the peculiar constitution of the ice of glaciers, that is, the ice which is formed by the compression and metamorphosis of snow "The ice of the glacier," he says, "is, as already remarked, composed of distinct particles. From a piece of this ice you can, as a general thing, easily remove the particles, one after the other, without injuring the surrounding ones; and, if you should find a particle which cannot be taken out without afflicting the rest, you will still notice that you can move it a little relatively to the others without harming them. Take a piece of the ice of the glaciers of a convenient size, and, in trying (so gently that it does not break) to twist or bend it, you will notice at once that there is a little changeableness in the minute portions of which it is composed."
Both M. de Seue and Prof. Sexe reject the theory of expansion as failing to account for the phenomenon of the glacier's progression, and both virtually agree in ascribing that progression to the combined influence of the enormous pressure exerted by the glacier's weight and the melting produced by the air. Unfortunately for the former theory—of expansion—it is difficult to see how it will explain the greater motion of the glacier in precisely that part of the year and of the day when the heat is the greatest, and the influence of expansion by freezing must necessarily be least operative.
The rapidity of the glacier's motion is much greater than we would naturally expect. By a course of very careful observations and measurements, Prof, Sexe found that, in the middle of July, 1868, the ice on the surface of the glacier of Boium, near the centre of the glacier and some distance from the lower end, moved 2041⁄2 inches (Norwegian) in 211 hours. This was about 97⁄100 of an inch per hour, and, if kept up during the entire year, would have given a total motion of about 707 feet. Here the motion was considerably greater by day than by night; in the former, exceeding 11⁄20 inch per hour, and, in the latter, being about 17⁄20 only. M. de Seue, however, coming later in the same month, when the weather was less uniformly pleasant, found the average rate of progression of the same point very much diminished, viz., to less than 3⁄4 of an inch per hour; and there is every reason to believe that, had these gentlemen been able to resume their observations in winter, they would have found that the motion during the cold weather is almost inappreciable. It is unnecessary to say that the difficulty of taking observations during half the year, on account of the temperature, and the glacier being covered over with deep snow, can scarcely be exaggerated.
It is not every part of the glacier which moves with even the rapidity mentioned. Toward the sides (and undoubtedly we should also find it so at the bottom, if we could get at it), the influence of friction can be detected retarding the motion. Near the lower end, also, the ice appeared to advance not more than one-third as fast as further up.
Of the numerous glaciers which M. de Seue describes as descending from the snow-field of Justedal, a number seem to be objects of great beauty. The photographic views which accompany his paper unfortunately fail to convey a very satisfactory idea of their appearance. The most considerable is the glacier of Trensbergdal, some nine miles long, and from two-thirds of a mile to nearly a mile in width. In several cases two or more glaciers meet, and, joining their contents, merge so thoroughly that they can be distinguished only by the moraines—lines of detached blocks of stone, torn from the rocks above in the downward course of the icy current, and which mark their edges even after their junction. Several are instances of what the French savants have called glaciers remaniés, the internal structure being altogether changed in consequence of their having been precipitated over ledges of rocks of considerable height. One of the smallest of the number is the glacier of Lunde, which is less than a mile in length, and only 100 feet in breadth. The interest attaching to it, however, lies in the suddenness with which it makes its spring down from the snow-field. From the opposite side of the valley it appears like a cascade suddenly congealed in its fall; and the wonder of the spectator is excited by the apparent impossibility that such a mass of ice should thus remain suspended in mid-air. A nearer approach dispels the illusion, but scarcely the amazement of the beholder; for, after all, the inclination of the glacier is at least 45° with the horizon, nor could it maintain itself in this position but for the steep banks that inclose it, and the large mass of ice at its base which props it up.
All the glaciers of the first class are remarkable for the circumstance that their lower extremities are so little raised above the level of the ocean. While the glacier of lökuls-fiord, in Northern Norway, is the only one in Europe, we believe, which actually comes down to the water's edge, there are several around Justedal that reach to within a few hundred feet of the sea's level, and one, that of Suphelle, to within 140 feet of it.
Of many other points developed in the valuable papers of Prof. Sexe and M. de Seue, which are of more interest to the student of physical geography and geology than to the general reader, we can enter into no discussion here.